1. Field of the Invention
The present invention relates generally to non-volatile semiconductor memory devices and particularly to those including a memory transistor having a floating gate.
2. Description of the Background Art
Conventionally, in flash memory, applying a fixed pulse voltage to a memory transistor at a control gate and making a decision as to whether the memory transistor's threshold voltage has reached a verify voltage are repeated to write a data signal.
There is also a method applying a fixed voltage to a memory transistor at a control gate and detecting that the memory transistor's drain current has reached a reference current, and ending a write (see U.S. Pat. No. 5,422,842 for example).
In conventional flash memory, however, when a memory transistor's control gate receives voltage the memory transistor has a large initial current flowing therethrough and the flash memory disadvantageously consumes a large current. Furthermore, the memory transistor's threshold voltage is excessively increased and threshold voltage's variation is disadvantageously increased.